The present invention relates to magnetic field sensors and, in particular, to Hall sensors for detecting spatial components of a magnetic field in a reference point, the sensors being in particular calibratable during measuring operation, and to the calibration and measuring methods employed here.
Apart from measuring magnetic fields as to magnitude and direction, Hall sensor elements which are based on the Hall effect are frequently employed in technology for non-contact contactless signal generators for detecting the position of switches or control elements in a wear-free manner. Another way of application is measuring a current, wherein a Hall sensor element is placed close to a conductive trace and measures, in a non-contact manner, the current in the conductive trace via detecting the magnetic field generated by the current in the conductive trace. In practical applications, Hall sensor elements excel, in particular, by their relatively great insensitivity to external influences, such as, for example, contaminations and the like.
In technology, both so-called horizontal or lateral Hall sensor elements and vertical Hall sensor elements are known, FIG. 6a exemplarily illustrating a horizontal Hall sensor element and FIG. 6b illustrating a known vertical Hall sensor element.
A Hall sensor element is generally made up of a semiconductor wafer having four contact terminals which are provided for an electrical connection to an external control circuit. Of the four contact terminals of a Hall sensor element, two contact terminals are provided for impressing an operating current through an active semiconductor region, whereas the other two contact terminals are provided for detecting the Hall voltage. When the semiconductor wafer through which the operating current flows is exposed to a magnetic field having an induction {right arrow over (B)}, the result will be a deflection in the current paths which is caused by the “Lorenz force” acting on the moved charge carriers in the magnetic field. The Hall voltage will be perpendicular to the direction of the current flow and perpendicular to the magnetic field applying in the active semiconductor region.
As is basically illustrated in FIG. 6a, a known horizontal Hall sensor element 600 is generally made up of an n-type doped semiconductor region 602 on a p-type doped semiconductor substrate 604. A Hall sensor element which is arranged in parallel to a chip surface (x-y plane) is referred to as horizontal.
The n-type doped active region 602 is typically connected to external control or evaluation logic via four contact electrodes 606a-d which are arranged in pairs opposite each other in the active region 602. The control or evaluation logic is not illustrated in FIG. 6 for clarity reasons. The four contact electrodes 606a-d are divided into two opposite control current contact electrodes 606a and 606c which are provided to generate a current flow IH through the active region 602, and additionally into two opposite voltage tapping contact electrodes 606b and 606d which are provided for tapping as a sensor signal a Hall voltage UH occurring in a magnetic field {right arrow over (B)} applying perpendicular to the current flow in the active region 602 and the magnetic field applying. By impressing the current flow IH between different contact electrodes and correspondingly tapping the Hall voltage UH at the other contact electrodes perpendicular to the current flow, compensation methods which allow compensating tolerances which occur in the Hall sensors, for example, due to manufacturing tolerances, etc., over several measuring cycles may be implemented.
As can be seen from the horizontal Hall sensor element 600 illustrated in FIG. 6a, the active region between the contact terminals 606a-d is defined such that the active region has an effective length L and an effective width W. The horizontal Hall sensor elements 600 illustrated in FIG. 6a are relatively easy to manufacture using conventional CMOS (Complementary Metal Oxide Semiconductor) processes for manufacturing semiconductor structures.
Apart from the horizontal Hall sensor elements, realizations of so-called vertical Hall sensor arrangements which also allow standard semiconductor manufacturing technologies, such as, for example, CMOS processes to be used, are also known. An example of a vertical Hall sensor element 620 is basically illustrated in FIG. 6b, wherein vertical here means a plane perpendicular to the plane of the chip surface (X-Y plane). In the vertical Hall sensor element 620 illustrated in FIG. 6b, the advantageously n-type doped active semiconductor region 622 extends in the form of a well in a p-type doped semiconductor substrate 624, the active semiconductor region 622 having a depth T. As is illustrated in FIG. 6b, the vertical Hall sensor element comprises three contact regions 626a-c which are arranged in the semiconductor substrate 624 adjacent to the main surface thereof, the contact terminals 626a-c being all arranged in the active semiconductor region 622. Due to the three contact regions, this variation of vertical Hall sensor elements is also referred to as 3-pin sensor.
The vertical Hall sensor element 620 illustrated in FIG. 6b also comprises three contact regions 626a-c along the main surface of the active semiconductor region 622, the contact region 626a being connected to a contact terminal A, the contact region 626b being connected to a contact terminal B and the contact region 626c being connected to a contact terminal C. When a voltage is applied between the two contact terminals A and C, the result will be a current flow IH through the active semiconductor region 622 and a Hall voltage UH which is oriented to be perpendicular to the current flow IH and to the magnetic field {right arrow over (B)} can be measured at the contact terminal B. The effectively active regions of the active semiconductor region 622 are predetermined by the depth T of the active semiconductor region 622 and the length L corresponding to the distance between the current feeding contact electrodes 626a and 626c. 
Horizontal and vertical Hall sensors and methods for reducing offsets which form due to element tolerances, such as, for example, contaminations, asymmetries, piezoelectric effects, aging phenomena, etc., like, for example, using the spinning-current method, are already known in literature, such as, for example, in R. S. Popovic, “Hall Effect Devices, Magnetic Sensors and Characterization of Semiconductors”, Adam Hilger, 1991, ISBN 0-7503-0096-5. Frequently, vertical sensors operated in a spinning-current manner are made up of two or of four individual sensors, as is described, for example, in DE 101 50 955 and DE 101 50 950.
In addition, apart from the variation of 3-pin vertical Hall sensor elements, there are so-called 5-pin vertical Hall sensor elements which are also described in DE 101 50 955 and DE 101 50 950. In 5-pin Hall sensor elements, too, there is a way of performing a measurement compensated for tolerances of individual elements by means of a compensation method extending over several measuring phases, wherein exemplarily a spinning-current method may also be employed here.
Spinning-current technique means continuously cyclically turning the measurement direction for detecting the Hall voltage at the Hall sensor element using a certain clock frequency by, for example, 90° and summing over all the measuring signals of a complete turn of 360°. In a Hall sensor element comprising four contact regions of which two respective contact regions are arranged in pairs to each other, each of the contact pairs is, depending on the spinning-current phase, used both as a control current contact region for feeding a current and as a measuring contact region for tapping the Hall signal. Thus, in a spinning-current phase or in a spinning-current cycle, the operating current (control current IH) flows between two associated contact regions, the Hall voltage being tapped at the other two contact regions associated to each other.
In the next cycle, the measuring direction is turned by 90°, so that the contact regions which, in the previous cycle, were used for tapping the Hall voltage, now serve for feeding the control current. By summing over all the four cycles or phases, the offset voltages due to manufacturing or material approximately cancel out one another, so that only the portions of the signal which really are dependent on the magnetic field will remain. This procedure is, of course, also applicable for a greater number of contact pairs, wherein exemplarily, with four contact pairs (comprising eight contact regions), the spinning-current phases are cyclically turned by 45° in order to be able to sum all the measuring signals over a full 360° turn.
In horizontal Hall sensors, four sensors are also frequently used, since, with a suitable arrangement, the offset can additionally be reduced significantly by spatial spinning-current operation, see, for example, DE 199 43 128.
When a magnetic field is to be measured for several spatial directions, separate Hall sensor elements are most frequently used. Using separate sensors, for example for detecting the three spatial directions of a magnetic field, generally entails the problem that the magnetic field to be measured is not measured in one point, but in three different points. FIG. 7 makes this aspect clear, FIG. 7 showing three Hall sensors 702, 704 and 706. The first Hall sensor 702 serves for detecting a y spatial component, the second Hall sensor 704 serves for detecting a z spatial component and the third Hall sensor 706 is provided for detecting an x spatial component. The individual sensors 702, 704 and 706 measure the corresponding spatial components of a magnetic field approximately in the respective central points of the individual sensors.
An individual sensor, in turn, may be made up of several Hall sensor elements. FIG. 7 exemplarily shows three individual sensors which each comprise four Hall sensor elements, wherein, in FIG. 7, a horizontal Hall sensor 704 detecting a z component of the magnetic field to be measured and one vertical Hall sensor 702 and 706 each for the y and x components of the magnetic field to be measured are assumed. The arrangement for detecting the spatial magnetic field components, as is exemplarily illustrated in FIG. 7, entails the problem that the magnetic field cannot be measured in one point, but in the respective central points of the individual sensors. This inevitably entails corruption, since an exact evaluation of the magnetic field based on the magnetic field components, detected at different locations, of the magnetic field sensor, is not possible.
Another aspect when detecting and evaluating magnetic fields by means of Hall sensor elements is calibration of the individual elements. According to conventional technology, Hall sensor elements are most frequently provided with so-called excitation lines which allow generating a defined magnetic field in the measuring point of an individual sensor in order to achieve the sensor to be calibrated subsequently by comparing and/or associating the Hall voltage measured to the defined magnetic field.
It is possible using excitation lines to generate an artificial magnetic field at a Hall sensor by means of which a simple wafer test, i.e. a test directly on the substrate, and a self-test and sensitivity calibration during operation are possible, compare Janez Trontelj, “Optimization of Integrated Magnetic Sensor by Mixed Signal Processing, Proceedings of the 16th IEEE Vol. 1. This is of particular interest in safety-critical sectors, such as, for example, in the automobile sector or also in medical engineering, since this allows the sensors to monitor themselves even during operation.
When exemplarily several individual sensors are used for detecting the spatial components of a magnetic field, as is exemplarily shown in FIG. 7, each individual sensor necessitates a corresponding excitation line for calibration, wherein the individual sensors are still calibrated individually. This means that the calibration effort is scaled depending on the number of individual sensor elements and, in the case of spatially detecting three magnetic field components, is increased by three compared to the calibration effort of an individual sensor.
One approach of allowing a magnetic field to be evaluated, i.e. detecting a measurement in one point, is a 3D sensor made by Ecole Polytechnique Federal Lausanne EPFL, compare C. Schott, R. S. Popovic, “Integrated 3D Hall Magnetic Field Sensor”, Transducers '99, June 7-10, Sensai, Japan, VOL. 1, pages 168-171, 1999. FIG. 8 is a schematic illustration of such a Hall sensor 800 implemented on a semiconductor substrate 802. The 3D sensor comprises four contact areas 804a-d via which currents can be impressed into the semiconductor substrate 802. The 3D sensor additionally comprises four measuring contact areas 806a-d via which the different magnetic field components can be detected. Wiring 810 is illustrated on the right side of FIG. 8. The wiring shown made up of four operational amplifiers 812a-d evaluates the Hall voltages proportional to the individual magnetic field components and outputs the corresponding components at the terminals 814a-c in the form of signals Vx, Vy and Vz.
The sensor illustrated entails the problem that it can only be calibrated by a defined magnetic field generated externally and has no excitation line of its own. Additionally, due to its set-up and its mode of functioning, this sensor cannot be operated using a compensation method, such as, for example, a spinning-current method. Furthermore, a problem of the arrangement shown in FIG. 8 is that such a semiconductor element, due to contaminations of the semiconductor material, asymmetries in contacting, variations in the crystalic structure, etc., exhibits offset voltages which cannot be suppressed using a corresponding compensation wiring suitable for spinning current. The sensor measures magnetic field components in a focused point, however, it exhibits a high offset and consequently is suitable for precise measurements to a limited extent only. FIG. 9 shows a compensation-enabled (spinning-current) 3D-sensor which detects spatial magnetic field components in one measuring point and is discussed by Enrico Schurig in “Highly Sensitive Vertical Hall Sensors in CMOS Technology”, Hartung-Gorre Verlag Konstanz, 2005, Reprinted from EPFL Thesis No. 3134 (2004), ISSN 1438-0609, ISBN 3-86628-023-8 WW. page 185ff. In the top part of FIG. 9, the 3D-sensor of FIG. 7 made up of three individual sensors is shown. FIG. 9, in the top part, shows three separate individual sensors 902, 904 and 906 for detecting the spatial magnetic field components. In FIG. 9, in the bottom part, an alternative arrangement of the individual sensors is shown. With this arrangement, the sensor 904 is maintained unchanged since the measuring point of the sensor 904 in FIG. 9 is in the center of the arrangement 900, additionally the two individual sensors 902 and 906 are made up of individual elements which are separable. The sensor 902 is now divided into two sensor parts 902a and 902b and symmetrically arranged around the central point of the sensor element 904. An analogue procedure is done for the sensor 906 so that this one, too, is divided into two sensor parts 906a and 906b which are symmetrically arranged around the central point of the sensor element 904, along the corresponding spatial axis. Due to the symmetrical arrangement of the individual sensor elements, the magnetic field is then detected in one point which is in the geometrical center of the arrangement.
In summary, one might say that individual sensors which are symmetrical arranged around a central point may be used in the field of conventional technology for measuring multidimensional magnetic fields. Arrangements of this kind can, in particular, be realized in angular sensors where a magnetic field is to be measured in one point by all the sensors. Monitoring, calibration and testing of the sensors, however, are problematic in these arrangements.